1. Field of the Invention
The present invention relates to a high-conductivity carbon thread usable as a light, conductive element, and, more particularly, to a graphitized carbon thread. The present invention also relates to a process for producing the high-conductivity carbon thread.
2. Related Background Art
Carbon or graphite threads are produced in a method comprising baking fibers of polyacrylonitrile (referred to as PAN) or by a method of melt-spinning a coal-originated or a petroleum pitch, subjecting the spun fiber to infusible treatment, then baking it, and, if necessary, further to effect thereon heat treatment at a high temperature for graphitization. The former is called PAN-type carbon fibers and the latter is called pitch-type fibers. These fibers are generally used for reinforcement. To obtain high elasticity and high strength, as many impurities, presenting a hindrance to the carbonization or the graphitization are removed as possible from the precursor material, i.e., PAN or pitch. However, the thus-produced carbon fibers using Such refined precursor materials do not show high enough conductivity after the graphitization. For example, a conductivity of about 1 x 10.sup.3 S/cm is common for PAN type carbon fibers, and about 2 x 10.sup.3 S/cm for pitch-type carbon fibers. It is considered that this low conductivity is due to insufficient spreading of the hexagonal carbon as a whole network even after the graphitization which allows many grain boundaries and defects to still exist.
On the other hand, vapor-phase growth carbon fibers, referred to as VGCF, obtained by thermal decomposition of gasified organic compound at a high temperature, show high conductivity, but generally have a short fiber length. Therefore, use of VGCF is limited. Among the known VGCF, the fibers described in Japanese Unexamined Patent Publication Tokkaisho 57-117622 are relatively long with an average diameter of 10 .mu.m and a length of approx. 20 cm. These fibers have satisfactory conductivity of 2 x 10.sup.4 S/cm after the graphitization. It is, however, difficult to use the VGCF as a conductive wire, since the fibers are discontinuous as well as lacking in mass-producibility.